Importance of Water in the Diet

 
Water.  Most of us take it for granted.  But have you every taken a moment to stop and think just how important water is to you?  For the human body, water is truly a vital resource.  You can go weeks without food but only 5-7 days without water.  When the water in your body is reduced by just 1 percent, you become thirsty.  At 5 percent, muscle strength and endurance declines significantly and you become hot and tired.  When the loss reaches 10 percent, delirium and blurred vision occur.  A 20 percent reduction results in death. 
 
There is no more important nutrient for our bodies than water.  No other substance is as widely involved in the processes and make up of the body.  A man's body is about 60 percent water, and a woman's is approximately 50 percent.  Did you know that the human brain is about 75 percent water? 
 
Tissue Percent Water
Blood 83.0
Heart 79.2
Muscle 75.6
Brain 74.8
Skin 72.0
Bone 22.0
 
Every day, we lose 2-3 quarts of water through urination, sweating and breathing.  Since many of the processes within the body rely greatly on water, it is important we replace our fluids regularly to compensate for this loss. 
 
Chem Window --- Water

Join us in an exploration of just some of the diverse roles water has in our bodies... 

Water as a Solvent: 

Water is the fundamental solvent for all biochemical processes in our bodies.  Because water is highly polar (has an unequal distribution of charge), it is an excellent solvent for other charged and polar molecules.  Hemoglobin, carbonates, various proteins, and many other molecules in the body use water as a solvent. 
 
Chem Window --- Solvation

Water as a Transporter: 

Once a substance is dissolved in water, water becomes very important for transporting it throughout the body.  Blood, which is 83 percent water, transports oxygen, CO2, nutrients, waste products, and more from cell to cell.  Urine is also mostly water. Another very important transporter, urine removes waste products from the body.  If we don't get enough water and can't produce enough urine, toxic levels of wastes build up in the body and we can become very sick or even die. 

Protection:  

Water is needed for protection as well.  It keeps your mouth moist and washes away dirt and grim on your eyes.  Water even lubricates our joints, keeping them from getting stiff and making sure motion is smooth. 

Chemical Reactant: 

As a chemical reactant, water is involved in many processes and pathways of the body.  We use it to digest food in the gastrointestinal tract, to access stored energy for muscles and organs, and for countless other reactions.  Next, we will examine one of these reactions in detail and see how water helps regulate pH in the body. 

pH regulation:  

Our bodies must maintain a very specific pH level of 7.4.  pH values less than 6.9 and greater than 7.6 are life threatening so it is essential that we have ways to keep pH from deviating too far from normal.  Water is a reactant in a very important reaction that maintains pH at 7.4. 
 
Chem Window --- pH

This reaction takes place in the blood: 

CO2 + H20 <==> H2CO3 <==> H+ + HCO3

Can you see water's role?  If pH is too high (too few H+ ions), water reacts with carbon dioxide to create more H+ ions, lowering the pH.  A pH lower than 7.4 shifts the above reaction to the left, using up H+ ions, creating CO2 and H2O and raising pH.   It is important that this reaction go back and forth to maintain equilibrium. 

Electrolyte Balance:  

Water is very important in maintaining electrolyte balance within our bodies.  Electrolytes are charged ions (such as Na+ or Cl-) which must be kept at certain levels to maintain the proper amount of water in our cells.  Electrolytes transmit all sorts of information to our brains in the form of nerve impulses and are important in muscular activity as well.  To maintain electrolytes at the proper level in our cells, water flows in and out of the cell to make sure that these ions remain in balance. 

Temperature Regulation:  

In our homes, the air conditioner keeps things cool.  But how does our body stay cool?  Well, we actually have our own natural air conditioning system.  Bet you can guess what it is... 

That's right, water!  The most important way water regulates our body temperature is through sweat.  Our normal body temperature is 98.6 degrees Fahrenheit.  When you go outside in the sun, you'll probably begin to sweat in no time, especially if you're active.  But why does the body need to sweat?  Sweat is a way for the body to cool itself down.  When we sweat, it evaporates on our skin, drawing heat away from the body and cooling us down. 

Exercise and Water: 

When we exercise, water loss through sweat can reach 1-2L per hour!  If you are exercising in warm weather, water should be replenished every 15 minutes in order to keep muscles strong and body temperature down.  This is especially crucial for long endurance events, which is why cyclists (who strip away every unnecessary ounce of equipment) still carry water with them. 

Water is vital in delivering oxygen to muscles and helps the body perform physical labor more efficiently.  Here are some graphs showing the effects of fluid replacement during exercise.  Can you guess which lines represent the people who were given water and which represent those who went without it? 
 
(Graphs showing decreased performance without water) 
 
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